package day09;

import java.util.Scanner;

/**
 * Created by Administrator on 2017/1/8.
 */
public class Test07 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long n = sc.nextLong();
        long sum = 0;
        for (long i = 1L; i <= n; i++) {
            sum += i;
        }
        System.out.println(sum);
    }
}
